Post by: vtsteam on March 08, 2025, 11:35:26 AM
What needs to be heated is the end of the stainless steel displacer tube -- heated area = approximately 1" long by 1" diameter (25mm x 25mm).
Temp of the cylinder wall should be some number in the region of say 250F - 450F (120C - 230C) -- not a critical number as long as it stays consistent. An electric heat source would be ideal for consistent heating.
I need something I can make myself from readily available materials or buy at low cost.
What's available:
1.)House voltage is US standard, 120 V.
2.) I have on hand various refractory materials that I've used in the past in my melting furnace, including fire clays and refractory mix, insulative blanket, and plaster of Paris.
3.) I also have stainless steel fishing leader of various fine diameters, which I've used as heated wire for cutting wing panels out of foam. That's generally performed at 12 V with a small power supply -- I think I was using .011" wire for that, but I don't think it lasts long. Definitely not used at red heat.
4.) I have various computer power supplies, transformers, wall warts, and a 10 amp variable DC power supply.
5.) However if a cheap ready made or salvage solution suggests itself to anyone -- I'm definitely open to that route.
Post by: awemawson on March 08, 2025, 03:16:41 PM
Post by: vtsteam on March 08, 2025, 04:19:45 PM
Unfortunately I don't have either Kapton tape or nichrome wire on hand.
Looks like Kapton is available on Amazon at reasonable price for the amount I would need. How hot does it allow the wire to get? Also nichrome wire is available there at not too bad a price either. But what gauge to get?
While casting about on Amazon looking up "heating coil" some small induction heaters showed up. Examples:
https://www.amazon.com/HURRISE-5V-12V-Induction-Heating-Frequency/dp/B09SV8N52X
https://www.amazon.com/Voltage-Induction-Heating-Module-Flyback/dp/B0BL767R3Q
But possible problems: some bad reviews, and how would a moving aluminum displacer with steel pushrod inside a stainless steel cylinder be affected by the alternating field? Also how big is "small", etc.
As a guess, induction may not be a great idea. Still it's cheap and easy to fit a coil around the end of the displacer cyl. But Probably straight resistance heat is best, right?? :zap:
Post by: vtsteam on March 08, 2025, 04:33:04 PM
It's a liner for a pouring cup for metal casting that I once made out of fireclay and sand. I packed it into a section of steel tubing, but since it sat for a couple years it shrank and released from it.
I was just hunting through scrap for something else I needed, and spied it sitting there loose in its tube. :med:
Post by: vtsteam on March 08, 2025, 07:08:34 PM
Making the coils was very difficult because the stainless leader material is extremely resistant to bending. It's basically a spring version of stainless steel. I couldn't get it to form a coil around a mandrel larger than 1/2" (12mm) diameter. So I resorted to just bending it by hand roughly to fit into the tube. A series of many small kinks to yield the ID. The springiness held it against the inside of the tube..
If I substitute nichrome wire, presumably it will be more bendable on a mandrel close to the ID of the tube (about 1.3", 33mm) --- I hope!
It looks from these experiments like I need about 150 watts to get the temperature in the range I wanted in that tube.
The heaviest leader material I have is .021" dia (.53 mm) -- and that was the best performer, and it starts to glow at about 5.5 amps.
That's all the info I have today.
Ideas and suggestions welcome.
Post by: vtsteam on March 08, 2025, 07:33:44 PM
Post by: vtsteam on March 08, 2025, 07:52:09 PM
https://www.amazon.com/Simple-Deluxe-Ceramic-Emitter-Reptile/dp/B0CWGCCQWV
It does say not to turn it on and off frequently.
How frequently? :scratch:
Post by: awemawson on March 09, 2025, 03:38:44 AM
Post by: vtsteam on March 09, 2025, 10:03:27 AM
I guess I need to have a ballpark idea of gauge needed.
I'd like to keep the voltage low on something I that I build for safety sake. 12 volts would be ideal, but that would require over ten amps (I believe -- not actually sure, but as a guess 120 watts might be minimum needed?). My variable DC power supply is a 10 amp supply, it does however go to 30V, so I guess I have the supply for it.
I'm not sure how nichrome wire compares with equivalent gauge stainless for resistance per unit length (when hot).
I did feel in my tests that I'd have liked even thicker ss wire, for fewer turns -- after all I only need to heat about an inch of length on the displacer cylinder. Lots of turns means closer spacing, which is harder to make.
I was thinking that I do have other stainless wire besides just the fishing leader. I have aircraft grade twist lock wire, and some other miscellaneous types. They probably all coil better as well. Might give samples of those a go. The power supply has both constant current and voltage modes, and the watt meter and IR temp probe makes it possible to test a short length and then extrapolate to longer.
Also, just for giggles I did send for those Herp warmer bulbs linked above. They are 2 for $9 for the 3" dia 150 watt versions, and I have a ceramic base incandescent light fixture.
Post by: vtsteam on March 09, 2025, 10:26:06 AM
Post by: vtsteam on March 09, 2025, 10:40:34 AM
One way to make a heater might be to wrap the wire around a waxed wood mandrel of say 1.5" (38mm) dia. Set that in a larger form and pour the mix over. Remove the mandrel when cured. If the form was rectangular and the mandrel located at the proper distance from the edges, it could be stood on edge and be the proper height for the displacer cylinder.
If the plaster of Paris does not prove to be heat resistant enough, I do have fire clay, and also Satanite as alternatives, though they are much less insulative.
Post by: tom osselton on March 09, 2025, 04:32:50 PM
Post by: vtsteam on March 10, 2025, 10:06:16 AM
Post by: tom osselton on March 10, 2025, 06:16:57 PM
Post by: Bluechip on March 11, 2025, 04:27:59 AM
https://www.ebay.co.uk/itm/325462059145?chn=ps&_ul=GB&mkevt=1&mkcid=28&google_free_listing_action=view_item&gQT=1 (https://www.ebay.co.uk/itm/325462059145?chn=ps&_ul=GB&mkevt=1&mkcid=28&google_free_listing_action=view_item&gQT=1)
Whether it has any relevance only you can decide.
:scratch:
Dave
Post by: shipto on March 11, 2025, 01:46:43 PM
Post by: vtsteam on March 12, 2025, 08:34:53 AM
I will also need to insulate around the heater, so kind of the opposite of the need for cooling on those immersion heaters. Thanks, though, I appreciate all suggestions! :beer:
Post by: vtsteam on March 12, 2025, 08:39:20 AM
what about a 3d printer hotend heater?
Dwayne, I don't know. I don't have one. I do kind of remember a hot air engine that was heated by I think some kind of soldering heater coil. It was in an old Model Engineer article -- back in the day when Dennis Chaddock was judging the Hot Air Engine Competition. I don't know if I'm remembering that correctly. I think the heater was used to prove out longevity of that modeler's engine. He ran it continuously, until deciding his electric bills were suffering!
:beer:
Post by: shipto on March 12, 2025, 01:42:32 PM
Post by: vtsteam on March 12, 2025, 06:38:53 PM
I did try the reptile heater, and that was a dismal failure. I tried letting it heat the displacer for 20 minutes and finally gave up.
That thing put out so little heat, I could actually hold my hand two inches in front of it, and it just felt warm. This despite all the manufacturer's dire warnings about minimum distances, and letting the bulb cool for an hour before handling it. It didn't even warm up the back of the firebox -- 1/8" steel plate a couple inches away, after 20 minutes.
Oh well. Maybe I can use it to keep greensand from freezing overnight in this early spring, in case I want to do some casting........ which I kinda do. .....been awhile....
Post by: vtsteam on March 18, 2025, 05:09:49 PM
To begin with, I found a piece of 1" PVC water pipe which had an OD of close to 1-1/2" (38mm) and cut off about a 3 inch (76 mm) length. I wrapped it with the safety wire and taped the coils in place. Then I crimped a couple wires onto the ends using some copper tubing and a wire crimper. The wires were high temp type salvaged from a dead oil filled electric radiator.
Post by: vtsteam on March 18, 2025, 05:17:53 PM
I painted Vaseline on the coil form as a release agent.
Post by: vtsteam on March 18, 2025, 05:25:03 PM
Oh, forgot to mention earlier, the bottom of the water pipe was covered with tape, so the plaster couldn't rise up inside.
A piece of masking tape was used to tie the sides of the mold box together to prevent bulging at the top.
Post by: vtsteam on March 18, 2025, 05:33:57 PM
I found that even with the weight of the heater and wires, it still wanted to float up sideways, pivoting on the wire. So I spooned sand into the pipe, which provided enough weight to keep it vertical.
Now to wait......
Post by: vtsteam on March 19, 2025, 09:47:30 AM
I figured that removing the core pipe might give me some problems because of the tape and I had thought of several clever ways to get it out of there. But giving it a simple twist with pliers back and forth a tiny amount, and pulling slowly freed it quite easily.
The coil of wire stayed in place. All in all a satisfying little job. Will it work to run the engine? No idea!
Post by: vtsteam on March 19, 2025, 09:53:15 AM
Variable power supply is going to probably be running about 15 volts, I'm guessing. It's a constant current type and max available is 10 amps. I'm thinking somewhere around 150 watts should be enough, but as yet, it's unknown.
Post by: vtsteam on March 22, 2025, 07:00:07 PM
I did a number of graduated tests of the heater starting at 30 watts, using the variable power supply. Temps were kept below 200 to start with in order to dry out any remaining moisture.
There was also some odor from a small amount of smoke as the tape, which held the original coil in place, and the small residue of release agent vaseline burned off. I did this outside on the porch for ventilation. All went well and the heater was a success when tested up to 90 watts, at 12 volts.
This was below the temperature where the stainless wire glows. I.believe that would be somewhere around 150 watts, as estimated earlier with wire tests. I'm really happy with the result, and I was able to run my No. 83 hot air engine on the heate in a test. (see that thread here: https://www.madmodder.net/index.php/topic,13865 ). :ddb: :ddb: :ddb: :dremel: